computer reboots

I had to reset the bios on my computer and now my computer will reboot itself without warning. I have an AMD Athlon XP 2000+ processor with a Biostar M7NCD motherboard. I am having problems getting the fsb up to 266mhz in bios. It will only allow me to go up to 200mhz. I looked at the manual and it says it allows up to 400mhz fsb.
Please Help

no I am not trying to overclock my pc. it was working fine until I had to reset the bios. I used the jumper next to the cmos battery. Anyways, I can choose my memory speed from 133 to auto. it is 333mhz. I have 512 ddr ram.

ok I set my fsb to 133, my comp still runs slow, n I set my fsb frequency to 133, I have that choice or auto. I've tried both. I set it to 133, when I put my mp3 player in it n load the software it will reboot. Any ideas?

Hy,
Get Memtest86, check your memory modules, see what happens then. Try also to get them out of the slots, clean them with a sheet of paper, put them back. See what's going on.
Check the power you have, with a multimeter, measure what voltage you have.
Re-install Windows.
Try another HDD.
Finally, if you can't get it working, set your entire computer on fire. Use gasoline
Just kidding about setting it on fire